#!/bin/bash
if [[ $# -ne 2 ]]
then
	echo 'Usage: cdx-chunk CDXFILE SIZE' >&2
	echo 'Returns offsets at which to split the WARC corresponding to CDXFILE such that each chunk is about SIZE bytes large.' >&2
	echo 'CDXFILE must be a IA-style modern CDX file (CDX N b a m s k r M S V g) for a single WARC file. DO NOT PASS ITEM CDX FILES!' >&2
	echo 'If CDXFILE ends with .gz, it is automatically decompressed. A dash may be passed to read from stdin, in which case it must be decompressed already.' >&2
	echo 'SIZE is an integer, optionally with a trailing M or G to designate MiB or GiB, respectively.' >&2
	echo 'The output is one integer per line, which designates the offset at which a new chunk begins. For example, if the first line is 1042, the first 1042 bytes are one chunk and the 1043rd byte begins the second chunk.' >&2
	echo 'Note that chunks may be much bigger than SIZE if there are large records in the WARC.' >&2
	exit 1
fi

file="$1"
declare -i size
if [[ "$2" == *M ]]
then
	size=$((${2::-1} * 1024 * 1024))
elif [[ "$2" == *G ]]
then
	size=$((${2::-1} * 1024 * 1024 * 1024))
else
	size=$2
fi
if [[ ${size} -eq 0 ]]
then
	echo "Error: invalid size" >&2
	exit 1
fi

{
	if [[ "${file}" == '-' ]]
	then
		cat
	elif [[ "${file}" == *.gz ]]
	then
		# Try to use zstdcat if available since it has much better performance.
		if command -v zstdcat &>/dev/null
		then
			zstdcat "${file}"
		else
			zcat "${file}"
		fi
	else
		cat "${file}"
	fi
} | \
  tail -n+2 | \
  awk '{ print $10 }' | \
  sort -n | \
  awk -v size=${size} '($1 - lastBoundary) >= size { print; lastBoundary = $1; }'